The OSS and 1.8 make a lot of difference, I mean 1.8 alone would, in low light.

When I just got my Nex and SEL50f1.8, I put it through paces vs my Canon DSLR with EF85/1.8 ( a legendary lens if you know Canon system well). No contest - in low light, EF simply couldn't keep up with OOS on SEL.

Now one area which I feel is a deficiency on SEL is the autofocus. It's just OK in good light, and can hunt and be slow in low light. It generally can't keep up with moving subjects in really low light. However, my Sigma primes aren't much better, besides by the time the light is low enough for it to start hunting, the Sigma won't be useable anyway.